Stub out a small portion of the x64 assembler.

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index 209aa2d3070e48da7890e9457e64fe4718cfd782..6e2c42a128ddb97bc2c634d9420561e37bb10db8 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -25,3 +25,12 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+#include "v8.h"
+
+#include "macro-assembler.h"
+
+namespace v8 { namespace internal {
+
+Register no_reg = { -1 };
+
+} }  // namespace v8::internal